The invention relates to an electropneumatic brake control device for controlling a parking brake of a vehicle having a service brake and a parking brake. It includes an electromagnetic valve device which is controlled by an electronic control device and can be supplied with compressed air from a compressed air store via a store connector, a parking brake signal terminal for inputting parking brake signals which are output by way of an electric parking brake signal transmitter, a valve device which is controlled pneumatically by the electromagnetic valve device and boosts the air quantity, with an operating output which can be connected to a first output connector for at least one spring brake cylinder. The operating output is ventilated in order to apply the at least one spring brake cylinder and is aerated in order to release it. A control air line is provided between an outlet of the electromagnetic valve device and a pneumatic control connector of the valve device which boosts the air quantity.
In electropneumatic brake control devices of this type, a failure of the electric power supply represents a problem because the electromagnetic valve device can then no longer be actuated. In addition, the electric parking brake signal transmitter also fails. It has therefore already been proposed to automatically ventilate the spring brake cylinders of the spring-loaded brake if the electric power supply fails. However, an emergency braking operation of this type is problematic during current driving because the vehicle can then come to a standstill at an unsuitable location and also because an emergency braking operation of this type takes place with rapid ventilation of the spring-loaded brake with a high braking force, there being the risk of a collision by following vehicles.
In order to solve this problem, EP 1 968 830 B1 proposes arranging a 3/2-way valve in the control line of the valve device (relay valve) which boosts the air quantity between the store connector and an electric bistable valve in the case of an electropneumatic brake control device of the generic type. It is possible for the bistable valve to be connected to the pneumatic control connector of the relay valve. In a passage position of the 3/2-way valve, the latter connects the store connector to the bistable valve and therefore to the control connector of the relay valve, in order to keep the spring-loaded brake released (driving position). In a ventilation position, the 3/2-way valve connects the bistable valve to a pressure sink (parked position), however, with the result that the pneumatic control connector of the relay valve is ventilated and, as a result, the spring-loaded brake is applied. The 3/2-way valve is controlled pneumatically by the supply pressure of the service brake in such a way that the passage or driving position is assumed if the supply pressure of the service brake exceeds a pressure threshold, but the ventilation or parked position is assumed if the supply pressure of the service brake undershoots the pressure threshold. In the case of an intact electric power supply, if the supply pressure in the compressed air stores drops owing to actuation of the service brake, the compressor counteracts this by way of additional delivery, with the result that the threshold value is not undershot in said circumstances. In the case of a failure of the electric power supply, however, the drive machine of the vehicle and therefore an additional delivery by way of the compressor fail as a rule, with the result that, if the service brake is actuated again, the compressed air stores of the service brake are emptied and, as a result, the supply pressure which acts as a control pressure for the 3/2-way valve falls below the threshold value. The 3/2-way valve then automatically switches into its ventilation or parked position, in which the spring-loaded brake is applied. Since the service brake has previously been actuated repeatedly, it is assumed that the vehicle is then already in a braked state or at a standstill, with the result that the abovementioned disadvantages might be avoided.
The invention is based on the object of developing an above-described electropneumatic brake control device in such a way that it has higher reliability with a simpler construction.
According to the invention, this and other objects are achieved by an electropneumatic brake control device for controlling a parking brake of a vehicle having a service brake and a parking brake, comprising:
a) an electromagnetic valve device which is controlled by an electronic control device and is supplied with compressed air from a compressed air store via a store connector;
b) a parking brake signal terminal for inputting parking brake signals which are output by way of an electric parking brake signal transmitter;
c) a valve device which is controlled pneumatically by the electromagnetic valve device and boosts the air quantity, with an operating output which can be connected to a first output connector for at least one spring brake cylinder, which operating output is ventilated in order to apply the at least one spring brake cylinder and is aerated in order to release it;
d) a control air line between an outlet of the electromagnetic valve device and a pneumatic control input of the valve device which boosts the air quantity;
e) a pneumatically controlled 2/2-way valve, with an inlet which is connectable or is connected to the control air line or to the operating output of the valve device which boosts the air quantity, an outlet which is connected to a pressure sink, and with a pneumatic control connector for a supply pressure of the service brake, wherein
f) the pneumatically controlled 2/2-way valve has two positions, a passage position which is set at a supply pressure of the service brake which is lower than a predefined pressure limit value and in which the inlet is connected to the outlet, and a shut-off position which is set at a supply pressure of the service brake which is greater than a predefined pressure limit value and in which the inlet is shut off with respect to the outlet.
The invention is distinguished by the pneumatically controlled 2/2-way valve, with an inlet which can be connected or is connected to the control air line or to the operating output of the valve device which boosts the air quantity, an outlet which is connected to a pressure sink, and with a pneumatic control connector for a supply pressure of the service brake, the pneumatically controlled 2/2-way valve having two positions, a passage position which is set at a supply pressure of the service brake which is lower than a predefined pressure limit value and in which the inlet is connected to the outlet, and a shut-off position which is set at a supply pressure of the service brake which is greater than a predefined pressure limit value and in which the inlet is shut off with respect to the outlet.
Here, the inlet of the pneumatically controlled 2/2-way valve can be connected or is connected, for example, directly or indirectly, for example via a further valve device, to the control air line or to the operating output of the valve device which boosts the air quantity.
Since all the solenoid valves of the electropneumatic brake control device are combined or arranged in the electromagnetic valve device, no solenoid valve is arranged in the control air line between the outlet of the electromagnetic valve device and the pneumatic control connector of the valve device which boosts the air quantity, the switching positions of which solenoid valve, which are dependent on energization or non-energization, might impede or prevent a flow connection between the outlet of the electromagnetic valve device and the pneumatic control connector of the valve device which boosts the air quantity by way of the control air line.
Firstly, a 2/2-way valve is therefore used instead of a 3/2-way valve for ventilation in the case of a failure of the electric power supply, which 2/2-way valve can be manufactured and assembled more simply.
Secondly, the 2/2-way valve is not arranged upstream of the solenoid valves of the electromagnetic valve device as in the prior art, as viewed from the supply air connector, but rather is arranged downstream thereof. Furthermore, the 2/2-way valve is then not connected in the control air line for the valve device which boosts the air quantity and is not connected in series in relation to the solenoid valves there, but rather is connected in a branch line which branches off from the control air line. This affords the further advantage that there are no longer any solenoid valves which are arranged downstream of the 2/2-way valve, the switching position of which might impede or prevent a ventilation of the pneumatic control connector of the valve device which boosts the air quantity. As a result, the functional security and reliability of the brake control device are increased.
With regard to the functionality of the electropneumatic brake control device, in the case of an intact electric power supply, if the supply pressure in the compressed air stores of the service brake circuit drops owing to actuation of the service brake, the compressor counteracts this by way of additional delivery, with the result that the pressure limit value is not undershot in said circumstances. As a result, the 2/2-way valve remains in or switches into the shut-off or driving position, in which the control air line of the valve device which boosts the air quantity is shut off with respect to the pressure sink.
In the case of a failure of the electric power supply, however, the additional delivery by way of the compressor fails, with the result that, in the case of a repeated actuation of the service brake, the compressed air stores of the service brake are emptied and, as a result, the supply pressure which acts as a control pressure for the 2/2-way valve falls below the pressure limit value. The 2/2-way valve then switches automatically, for example by way of spring loading, into its ventilation or parked position, in which the control air line is ventilated and the spring-loaded brake or the spring brake cylinders which are connected to the operating connector of the valve device which boosts the air quantity are applied, in order to apply the parking brake. Since the service brake has previously been actuated repeatedly, it is assumed that the vehicle is already in a braked state or at a standstill. As a result, it is ensured with high probability that, in the case of a failure of the electric power supply, the parking brake is engaged automatically only at a standstill of the vehicle.
The 2/2-way valve is preferably formed by way of a diaphragm valve, the opening pressure of which can be set in a simple way, for example by way of a spring, the prestress of which can be set.
According to one development, the electropneumatic brake control device represents one structural unit, it being possible for the 2/2-way valve to be integrated into the structural unit or not.
The 2/2-way valve is particularly preferably spring-loaded into the passage position counter to the action of a supply pressure of the service brake which prevails at the pneumatic control connector. If the supply pressure of the service brake then falls below the pressure limit value, the spring loading of the valve member ensures an automatic switchover of the 2/2-way valve into the passage or ventilation position.
The electropneumatic brake control device particularly preferably has at least one second output connector for a trailer control valve, the valve device being connected to the control air line and being configured such that it outputs a pressure signal which represents the parked state to the second output connector in the case of a pressure drop in the control air line which is brought about by way of the passage position of the pneumatically controlled 2/2-way valve. Said pressure signal can consist of an aeration or ventilation signal. Since trailer control valves act in an inverting manner in relation to the input pressure, in the case of switching of the 2/2-way valve, brought about by way of the failure of the electric power supply, into the passage or parked position by way of the electromagnetic valve device, into which the pressure drop in the control air line which is brought about as a result is fed back, the control pressure at the second output connector for the trailer control valve is reduced, for example, and the brake pressure for the service brakes in the trailer is increased to application pressure as a result. As a result, in the case of a failure of the electric power supply, not only are the spring brake cylinders of the tractor vehicle applied, but rather the service brakes of the trailer are also applied automatically.
The pressure sink can be formed, for example, by way of a ventilating connector which opens to atmosphere or by way of at least one compressed air store, in particular by way of a compressed air store of a service brake circuit which is then ventilated or has already been ventilated on account of the failure of the power supply, with the result that there is the necessary pressure gradient between the control air line and the compressed air store.
When, in particular, the pressure sink is formed by way of at least one compressed air store, a check valve is arranged in a compressed air connection between the inlet of the 2/2-way valve and the control air line according to one development, by way of which check valve a desired compressed air flow from the control air line to the inlet of the 2/2-way valve or to the pressure sink is made possible in the passage position, but an undesired compressed air flow from the inlet or the pressure sink into the control air line is suppressed.
The invention also relates to an electropneumatic brake system of a vehicle having a service brake and a parking brake, in particular of a heavy commercial vehicle with trailer operation, the service brake having a brake pedal and at least one compressed air store which is supplied with compressed air by a compressor and from which compressed air can be input in a manner which is dependent on an actuation of the brake pedal into service brake cylinders which can be actuated by compressed air. The parking brake has an electric parking brake signal transmitter which inputs parking brake signals into the signal terminal of an above-described electropneumatic brake control device, the first output connector of which is connected to at least one spring brake cylinder, the pneumatic control connector of the 2/2-way valve being connected indirectly or directly to the at least one compressed air store of the service brake. In this context, an indirect connection means that elements such as pressure limiting valves, overflow valves, shuttle valves or the like can be connected between the pneumatic control connector of the 2/2-way valve and the at least one compressed air store, which elements ensure that the supply pressure which prevails at the pneumatic control connector is influenced or changed. In the case of a direct connection, in contrast, the supply pressure of the at least one compressed air store prevails at the pneumatic control connector of the 2/2-way valve in an unchanged manner.
In customary electropneumatic brake systems such as EBS systems (electronic braking system), there are usually at least two service brake circuits with in each case one dedicated compressed air store, namely a first service brake circuit with a first compressed air store and a second service brake circuit with a second compressed air store. In an electropneumatic brake system of this type, a selection device is then preferably provided for forwarding the higher supply pressure of the supply pressures of the compressed air stores (first compressed air store, second compressed air store) to the pneumatic control connector of the 2/2-way valve, with a first inlet which is connected to the first compressed air store of the first service brake circuit, a second inlet which is connected to the second compressed air store of the second service brake circuit, and an outlet which is connected to the pneumatic control connector of the 2/2-way valve. Said selection device is formed, for example, by way of a shuttle valve which then forms a logical OR gate.
As a result of the measures, the control pressure for the 2/2-way valve is formed by way of the respectively higher supply pressure of the service brake circuits, with the result that a failure of a single service brake circuit, for example on account of a leak, does not already lead to a supply pressure in said service brake circuit which lies below the pressure limit value and then leads to an unnecessary switchover of the 2/2-way valve into the passage or parked position, since there does not necessarily also have to be a failure of the electric power supply in a leakage case of this type. Said measures therefore improve the functional reliability of the electropneumatic brake system.
According to one development, in each case one throttle device is provided between the first compressed air store and the first inlet of the selection device and between the second compressed air store and the second inlet of the selection device, the throttle cross section of which throttle device is at least so small that a volumetric flow which has occurred unintentionally between the first inlet and the second inlet of the selection device is smaller than a minimum delivery volumetric flow which the compressor is capable of additionally delivering into the compressed air stores at a minimum delivery output. An undesired volumetric flow of this type between the first inlet and the second inlet of the selection device can be produced, for example, by way of an intermediate position of the selection device or the shuttle valve. Said measures therefore improve the functional reliability of the electropneumatic brake system.
The invention also relates to a vehicle, comprising an above-described electropneumatic brake system, in particular to a tractor vehicle which is equipped for trailer operation having a trailer control valve.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.